Learn how to execute a spatial query to access polygon features from a feature service.
A feature layer can contain a large number of features stored in ArcGIS. To access a subset of these features, you can execute an SQL or spatial query, either together or individually. The results can contain the attributes, geometry, or both for each record. SQL and spatial queries are useful when a feature layer is very large and you want to access only a subset of its data.
In this tutorial, you use GL Draw to sketch a feature on the map, and then use ArcGIS REST JS to perform a spatial query against the LA County Parcels hosted feature layer. The layer contains ±2.4 million features. The spatial query returns all of the parcels that intersect the sketched feature. A pop-up is also used to display feature attributes.
To access location services, you need an API key or OAuth 2.0 access token. To learn how to create and scope your key, visit the Create an API key tutorial.
Go to your dashboard to get an API key. The API key must be scoped to access the services used in this tutorial.
In CodePen, update apiKey to use your key.
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const apiKey = "YOUR_API_KEY";
const basemapEnum = "ArcGIS:Streets";
const map = new maplibregl.Map({
container: "map", // the id of the div elementstyle: `https://basemaps-api.arcgis.com/arcgis/rest/services/styles/${basemapEnum}?type=style&token=${apiKey}`,
zoom: 12, // starting zoomcenter: [-118.805, 34.027] // starting location [longitude, latitude]});
Add script references
This tutorial uses three sets of libraries. ArcGIS REST JS is used for querying the feature layer. Mapbox GL Draw provides drawing tools, allowing the user to define a point, line, or polygon of interest. Terraformer is used to convert GeoJSON features generated by Mapbox GL Draw into ArcGIS JSON geometries; a requirement to query the feature layer service.
To display the Mapbox GL Draw controls, create a MapboxDraw and call map.addControl. By default, other tools are included, so you need to specify the three required tools: point, line, and polygon.
Three layers are required to display the three types of query you can perform: circle, line, and fill. They share a single GeoJSON source, which at any time will contain one feature of either Point, LineString or Polygon geometry. Create the source with an empty GeoJSON feature collection.
A line layer can display both line features and the border of polygon features.
The circle layer should be filtered to only display point features. Otherwise, a circle will be shown at each vertex of line and polygon features. You can use a filter and the ['geometry-type'] expression. See the MapLibre Style Specification for more details.
Similarly, the fill layer should be filtered to only display polygon features. Otherwise, line features will be treated as polygons and filled inappropriately.
Create an addQueryLayers function. Inside, add a GeoJSON source and circle, line, and fill layers
Mapbox GL Draw emits a draw.create event when you have finished drawing a feature. You can listen to this event to respond to the newly created feature.
By default, Mapbox GL Draw keeps all previously drawn features visible in its own layer. To prevent this, use deleteAll after copying the feature.
Add an event handler for draw.create. Inside, store the feature in the query layer, then delete all features from Mapbox GL Draw.
Click Run at the top right to test your code. You should be able to sketch a point, line or polygon feature, and see it turn into a green feature when complete.
When the matching parcels are returned, you can call setData on the parcels source to display them.
Create a function called executeQuery with geometry and geometryType parameters. Inside, create a new arcgisRest.ApiKeyManager to access the feature service. Call arcgisRest.queryFeatures. Pass the geometry and geometryType. Specify GeoJSON as the return type, requesting returnGeometry and specific outFields. All of the features within the geometry will be returned with attribute information set by the outFields property.
There are many other spatial relationships that you can specify with spatialRel. For example, you can use esriSpatialRelContains to only return parcels within the sketched polygon. See the ArcGIS services reference for details.
At the top right, click Run. When you create a feature using the toolbox, a spatial query will run against the feature layer and display all land parcels within the boundary of the feature.
Add a pop-up
You can add a pop-up to view attributes of a parcel when you click on it.
Add a click event handler to the parcels-fill layer. Inside, construct the pop-up content from the attributes of the clicked parcel.
When you click on the map to draw a polygon, a spatial query will run against the feature layer and display all land parcels that intersect the boundary of the feature. You can click on a parcel to see a pop-up with information about the parcel, or click somewhere else to reset the map.
